Teixeira Alexandre, Tahiri-Alaoui Abdessamad, West Steve, Thomas Benjamin, Ramadass Aroul, Martianov Igor, Dye Mick, James William, Proudfoot Nick J, Akoulitchev Alexandre
Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK.
Nature. 2004 Nov 25;432(7016):526-30. doi: 10.1038/nature03032.
New evidence indicates that termination of transcription is an important regulatory step, closely related to transcriptional interference and even transcriptional initiation. However, how this occurs is poorly understood. Recently, in vivo analysis of transcriptional termination for the human beta-globin gene revealed a new phenomenon--co-transcriptional cleavage (CoTC). This primary cleavage event within beta-globin pre-messenger RNA, downstream of the poly(A) site, is critical for efficient transcriptional termination by RNA polymerase II. Here we show that the CoTC process in the human beta-globin gene involves an RNA self-cleaving activity. We characterize the autocatalytic core of the CoTC ribozyme and show its functional role in efficient termination in vivo. The identified core CoTC is highly conserved in the 3' flanking regions of other primate beta-globin genes. Functionally, it resembles the 3' processive, self-cleaving ribozymes described for the protein-encoding genes from the myxomycetes Didymium iridis and Physarum polycephalum, indicating evolutionary conservation of this molecular process. We predict that regulated autocatalytic cleavage elements within pre-mRNAs may be a general phenomenon and that functionally it may provide the entry point for exonucleases involved in mRNA maturation, turnover and, in particular, transcriptional termination.
新证据表明转录终止是一个重要的调控步骤，与转录干扰甚至转录起始密切相关。然而，其发生机制却鲜为人知。最近，对人类β-珠蛋白基因转录终止的体内分析揭示了一种新现象——共转录切割（CoTC）。这种在β-珠蛋白前体信使核糖核酸中位于多聚腺苷酸化位点下游的初级切割事件，对于RNA聚合酶II高效转录终止至关重要。在此，我们表明人类β-珠蛋白基因中的CoTC过程涉及一种RNA自我切割活性。我们对CoTC核酶的自催化核心进行了表征，并展示了其在体内高效终止中的功能作用。所鉴定的核心CoTC在其他灵长类β-珠蛋白基因的3'侧翼区域高度保守。在功能上，它类似于为黏菌双孢绒泡菌和多头绒泡菌的蛋白质编码基因所描述的3'进行性、自我切割核酶，表明这一分子过程具有进化保守性。我们预测前体信使核糖核酸内受调控的自催化切割元件可能是一种普遍现象，并且在功能上它可能为参与信使核糖核酸成熟、周转，尤其是转录终止的核酸外切酶提供切入点。
